The invention relates to an engine control system for a vehicle having an automatic transmission, with a torque converter, at the power output side of the engine.
In such a vehicle, if the accelerator pedal is depressed when the automatic transmission is in a running range (such as a D range) or the like and the vehicle is stopped due to braking or a curbstone, the rotational difference between the input side and the output side of the torque converter, that is, the slip, becomes large. If this condition continues, the amount of heat generated inside the torque converter becomes large which may cause thermal deterioration of the torque converter or cause the torque converter to stall.
Japanese Patent Provisional Publication No. 60-4433 discloses an engine control system for preventing thermal deterioration of a torque converter. In this publication, when a shift lever is shifted from a stopping range to a running range, and the accelerator is depressed while the vehicle is stopped, the torque is immediately reduced (that is, immediately upon operation of the shift lever to the drive range). Torque is reduced by decreasing the fuel injection amount, or decreasing the amount of intake air, to place the engine in an idling condition and place the automatic transmission into an engaging condition.
However, in such a conventional engine control system, a range changeover signal for the automatic transmission must be input to the engine control system. This complicates the circuit arrangement. Also, if the range changeover signal is abnormal, the control described above becomes disabled.